Water-soluble group III polyether acid salt complexes and thin films from same

ABSTRACT

A water-stable and water-soluble ceramic precursor is provided, containing at least one Group III element. Also, a metal acid salt complex is provided comprising (1) bismuth, lanthanum, and titanium, and (2) a polyether acid. In addition, methods are provided for preparing the Group III metal acid salt complex and the Bi, La, Ti acid salt complex comprising a bismuth polyether acid salt complex, a lanthanum polyether acid salt complex, and a titanium polyether acid salt complex. Finally, devices that include lanthanum-doped bismuth titanate as the active component are provided, as well as a water-stable and water-soluble gallium polyether acid complex.

TECHNICAL FIELD

The present invention relates generally to improved ceramic precursorsand specifically to ceramic precursors for fabricating Group III solubleceramic precursor materials useful for making thin films, coatings,thick films and bulk ceramic materials, as well as polyether acidgallium materials which have interest for oral delivery of gallium whichhas been shown to be a therapeutic agents for certain cancers and toprotect bone.

BACKGROUND ART

Group III-based ceramic materials have a variety of uses. Examples ofGroup III materials include (1) alumina (Al₂O₃), (2) ferroelectriclanthanide-containing materials, such as bismuth lanthanum titanate(BLT), and (3) gallium compounds.

In particular, of concern are the synthesis, processing, and fabricationof the Group III-based materials into thin films, coatings, thick films,and bulk ceramic materials for, e.g., electronic devices and, in thecase of gallium, for oral delivery (gallium has been shown to be atherapeutic agent for certain cancers and for protecting bone).

Metal-organic decomposition (MOD) deposition processes are known for anumber of ceramic materials. The MOD process typically involves thesynthesis of thin film ceramics from metal organic acid salts (mostlyaliphatic acids such as neo-decanoic acid or 2-ethylhexanoic acid). TheMOD process is described in, for example, (1) U.S. Pat. No. 5,721,009,“Controlled Carbon Content MOD Precursor Materials Using Organic AcidAnhydride”, issued to Thomas K. Dougherty et al on Feb. 24, 1998; (2) J.V. Mantese et al, “Metalorganic Deposition (MOD): A Nonvacuum, Spin-on,Liquid-Based, Thin Film Method”, MRS Bulletin, pp. 48-53 (October 1989);(3) WO 93/12538, “Process for Fabricating Layered SuperlatticeMaterials”, filed in the names of Carlos A. Paz de Araujo et al,published on 24 Jun. 1993; (4) U.S. Pat. Nos. 5,434,102 (issued on Jul.18, 1995) and 5,439,845 (issued on Aug. 8, 1995), to Hitoshi Watanabe etal and both entitled “Process for Fabricating Layered SuperlatticeMaterials and Making Electronic Devices Including Same”; and (5) G. M.Vest et al, “Synthesis of Metallo-Organic Compounds for MOD Powders andFilms”, Materials Research Society Symposium Proceedinqs, Vol. 60, pp.35-42 (1986).

The present inventors and associates have continued their work in thisarea, culminating in (1) U.S. Pat. No. 6,054,600, “Non-Toxic SolventSoluble Group IV and V Metal Acid Salt Complexes Using Polyether AcidAnhydrides”, issued to T. Kirk Dougherty et al on Apr. 25, 2000; (2)U.S. Pat. No. 6,303,804, “Environmentally Benign Bismuth-ContainingSpin-on Precursor Materials”, issued to T. Kirk Dougherty et al on Oct.16, 2001; (3) U.S. Pat. No. 6,316,651, “Environmentally Benign Group IIand Group IV or V Spin-on Precursor Materials”, issued to T. KirkDougherty et al on Nov. 13, 2001, and (4) application Ser. No.10/771,066, filed Feb. 2, 2004. The contents of these patents and patentapplication are incorporated herein by reference.

Similar alumina-forming polyether acid materials have been described byBarron in, for example, U.S. Pat. No. 6,322,890, and Chem. Mater., Vol.9, pp. 2418-2433 (1997) useful as ceramic binders and fillers and aspolymerization catalysts. In this case, the materials are formed by ahigh temperature reaction of the free acids with alumina minerals thattakes a long time. Thus, the materials of Barron do not appear to be aseasy to make, as soluble or as easy to characterize and process as thealumina materials as described herein.

Lanthanum-doped bismuth titanate (BLT) is a newer ferroelectric materialthat has recently been developed. BLT prior art includes Park et al,Nature, Vol. 401, pp. 682-684 (October 1999); Bao et al, J. Appl. Phys.,Vol. 93(1), pp. 497-503 (1 Jan. 2003); and Kojima et al, J. Appl. Phys.,Vol. 93(3), pp. 1707-1712 (1 Feb. 2003).

Of note is a single reference for the yttria precursors of thepoly-ether acids, namely, Apblett et al in Phosphorous, Sulfur andSilicon, Vol. 93-94, pp. 481-482 (1994).

Finally, gallium maltolate is being investigated as a water-stable andsoluble oral delivery mechanism for gallium. The use of gallium organicsalts for therapeutic uses is desirable if these materials can be madeeasier to synthesize and characterize than presently. Further, it wouldbe desirable to tailor the gallium compounds as to bioavailability.

Thus, there remains a need for a soluble Group III containing precursorwhich is compatible and soluble in non-toxic and environmentally benignsolvents (including water), has unlimited stability and shelf life, andprovides high quality Group III-containing films and materials.

DISCLOSURE OF INVENTION

In accordance with the present invention, a water-stable andwater-soluble ceramic precursor is provided, containing at least oneGroup III element.

Further in accordance with the present invention, a metal acid saltcomplex is provided comprising (1) lanthanum, bismuth, and titanium, and(2) a polyether acid.

Still further in accordance with the present invention, a method ofpreparing a Group III metal acid salt complex is provided. The methodcomprises either:

-   -   combining at least one Group III metal salt and a polyether        acid; or    -   combining (1) at least one Group III metal alkoxide, (2) a        polyether acid anhydride, and, optionally, (3) a polyether acid.

Yet further in accordance with the present invention, a process isprovided for preparing a metal acid salt complex comprising a bismuthpolyether acid salt complex, a lanthanum polyether acid salt complex,and a titanium polyether acid salt complex, the process comprising:

-   -   preparing the bismuth polyether acid salt complex;    -   preparing the lanthanum polyether acid salt complex;    -   preparing the titanium polyether acid salt complex; and    -   combining the bismuth polyether acid salt complex, the lanthanum        polyether acid complex, and the titanium polyether acid salt        complex.

Still further in accordance with the present invention, a device isprovided that includes lanthanum-doped bismuth titanate as its activecomponent, the lanthanum-doped bismuth titanate prepared using a ceramicprecursor that contains at least one metal polyether acid salt complex.

Yet further in accordance with the present invention, a device isprovided that includes lanthanum-doped bismuth titanate as its activecomponent, the lanthanum-doped bismuth titanate prepared using a metalacid salt complex comprising (1) lanthanum, bismuth, and titanium, and(2) a polyether acid.

Further in accordance with the present invention, a water-stable andwater-soluble gallium polyether acid complex is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole FIGURE is a plot on coordinates of polarization (in μC/cm²) andvoltage (in V), depicting the hysteretic properties of a bismuthlanthanum titanate thin film ferroelectric capacitor, prepared inaccordance with the teachings herein.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention is directed to the synthesis, processing andfabrication into thin film electronic devices of several Group IIIsoluble ceramic precursor materials useful for making thin films,coatings, thick films and bulk ceramic materials. Examples includealumina and the ferroelectric lanthanide containing materials, aspecific example of which is bismuth lanthanum titanate (BLT). Thematerials are water-stable and water-processable and have a high solidscontent as compared to the prior art materials. Also described arepoly-ether acid gallium materials which have interest for oral deliveryof gallium which has been shown to be a therapeutic agents for certaincancers and to protect bone.

The present invention is a continuation of the present inventors' workin water-stable and processable ceramic precursors materials bestexemplified by above-referenced U.S. Pat. No. 6,054,600, which disclosesand claims the formation of Group IV and V materials. The presentdisclosure describes the Group III materials and their use in, forexample, the production of ferroelectric thin films in the case oflanthanum. The present disclosure also describes the aluminum precursorsthat yield alumina thin films, coatings and bulk ceramics. The presentinvention provides a more convenient and chemically controlled entry tothese precursors and is more general throughout the Group III materials,which provide a more processable form of aluminum precursors as comparedto the Barron derivatives.

The present invention describes the use of the specific polyether acidmetal salts of aluminum, lanthanum and gallium and in general the GroupIII metals. These materials have uses both in new electronic materialapplications and devices and the systems which use them. In addition,the materials described herein may offer additional advantages and newentries to water-soluble complexes for these elements. For example,water-soluble gallium compounds are of interest as, for example, oraltherapeutic agents for cancer and other maladies.

Thus, utility of the entire set of patents is much more general than thecurrent use for electronic devices, and these Group III materialsimprove upon the prior art in a broad range of applications.

The present invention provides the Group III elements in water-solubleand stable form, providing:

-   -   1. Lanthanum, and analogously the entire lanthanide group, as        new ceramic precursors useful as ferroelectric thin films.    -   2. Aluminum, and thus the alumina precursors, useful as coatings        (for example, optical coatings), thin films, and as binders and        processing aids for bulk alumina ceramics (alumina being one of        the more widely used bulk ceramics).    -   3. Gallium, and water-soluble gallium compounds, which are being        investigated as a cancer therapeutic agents.

These water-soluble and stable elemental materials may provide a numberof other therapeutic agents, depending on the stability andbioavailability of the materials. It maybe the case that the chemicaltailoring available by use of the different size polyether acid ligandsmay be used to tune the bioavailability.

Formulae (I)-(III) below depict three generic Group III compounds, whereM is a Group III metal. In the case of M=Ga, these compounds may havetuned stability and transport properties across bio membranes.

Applications for these ceramic precursor materials include, but are notlimited to, ferroelectric memories, Group III-containing materials,binders, and reactive fillers in ceramic processing, other thin andthick film devices, and anywhere where water-stable ceramic (or mineral)precursors might see use.

The present invention provides for the Group III materials compatiblewith less toxic solvents useful for manufacture of these and otherproducts as well as new products.

In one embodiment, BLT (lanthanum-doped bismuth titanate) thin films areprovided, which may be used in ferroelectric memories.

Applicants have also prepared a water-soluble alumina precursor, whichis an important new material which is easier to make, better controlledand characterizable and has improved processing and solubilitycharacteristics than the Barron materials described above.

In accordance with the present invention, Group III metal acid saltcomplexes are provided comprising a complex of at least one Group IIImetal alkoxide and a polyether acid. The Group III metal acid saltcomplexes are prepared by either (a) combining the Group III salt(s)with a polyether acid or (b) combining the Group III metal alkoxide(s),a polyether acid anhydride, and, optionally, the polyether acid.

The present invention is directed to the use of (a) the metal salts ofGroup III elements, e.g., Al, Ga, In, Tl, Sc, Y, La, the lanthanides,Ac, and the actinides, and other metals with a polyether acid and (b)the metal alkoxides of the Group III elements and other metals with apolyether acid anhydride (plus, optionally, the polyether acid) toproduce new ceramic precursors and materials and devices therefrom

Examples of the metal salts include, but are not limited to, the simpleorganic metal salts, such as the corresponding acetates, carbonates, andhydroxides. Examples of the metal alkoxides include, but are not limitedto, the lower metal alkoxides, such as methoxides, ethoxides,propoxides, and butoxides.

Essentially, the polyether acids useful in the practice of the presentinvention are polyethers of ethylene glycol, having the formulaCH₃O(CH₂CH₂O)_(n)CH₂COOHwhere n is 0 to 2.

The Group III metal polyether salt is represented by the followingstructure

where “Metal” is selected from a Group III element (as listed above), mis 3, and p is independently 0, 1 or 2 for each of the three ligands.

Mixed metal acid salt complexes are also contemplated herein, such asmixtures of bismuth, lanthanum, and titanium for fabricating BLT thinfilm ferroelectric memories. In that case, m is 3 for both bismuth andlanthanum and is 4 for titanium. For titanium, there thus are fourligands, and p is 0, 1 or 2 for each of the four ligands.

Examples of the polyether acids used to make the polyether acidanhydride include, but are not limited to, methoxyacetic acid,ethoxyacetic acid, methoxyethoxyacetic acid, andmethoxyethoxyethoxyacetic acid.

The solvents preferably used in formulating the complexes include, butare not limited to, 2-propanol and water, which are considerably lesstoxic than xylenes and n-butyl acetate often used. However, other polar,non-toxic solvents, such as low molecular weight alcohols, may also beemployed in the practice of the present invention. The low molecularweight alcohols have no more than five carbon atoms.

The general synthetic route to preparing metal acid salt complexes frommetal salts and polyether acid is as follows:

-   -   1. Combine the metal salt(s) with the polyether acid.

The metal salt used may comprise any of the known salts for that metal,including, but not limited to the salts listed above, namely, acetate,carbonate, or hydroxide.

The general synthetic route to preparing metal acid salt complexes frommetal alkoxide complexes is as follows:

-   -   1. Prepare the polyether acid anhydride from the corresponding        polyether acid by combining the polyether acid with a        dehydrating agent; and    -   2. Combine the polyether acid anhydride and the metal alkoxide.        In some embodiments, it may be desirable to also include the        corresponding polyether acid in the mixture.

The dehydrating agent used in the first reaction may comprise any of theknown dehydrating agents used to convert organic acids to thecorresponding anhydride. Examples include, but are not limited to,acetic anhydride and dicyclohexylcarbodiimide.

The metal alkoxide used in the second reaction may comprise any of theknown alkoxides for that metal.

The aluminum polyether acid salt complexes of the present invention areprovided by reacting an aluminum alkoxide material (in a specificexample, the aluminum sec-butoxide) with a polyether acid anhydride.Similar alumina-forming polyether acid materials have been described byBarron, as mentioned above. In the Barron work, the materials are formedby lengthy and high temperature reaction of the free acids with aluminaminerals and as described by Barron are alumoxanes, which are aluminumoxygen cage materials with various polyether acid ligands attached thatare difficult to fully characterize. Thus, the materials of Barron arenot as easy to make, as soluble or as easy to characterize and processas the alumina materials as described in the present invention.

EXAMPLES Synthesis of Aluminum(III)-Methoxyacetate-Methoxyethoxyacetate

To aluminum-s-butoxide (182.4 grams, 0.74 mol, Geleste AKA020) was addeda mixture of methoxyacetic anhydride (124 grams, 0.76 mol) andmethoxyethoxyacetic anhydride (292 grams, 1.17 mol). After stirring atroom temperature for twenty minutes, the reaction mixture was heated to150° C., stirred for 30 min. and allowed to stir and cool overnight. Thenext day, the liquid reaction mixture was concentrated on a rotaryevaporator to yield the product as a water stable and completelymiscible amorphous solid (287 grams of material, 6.96% Al calc.). Found13% alumina as measured by TGA (thermogravimetric analysis), calc.13.14%. IR(thin film) 3432, 3056, 2970, 2908, 2389, 2113, 1960 cm⁻¹.

Synthesis of Gallium(III)-Methoxyacetate

To gallium ethoxide (1.56 gram, 0.0076 mol, AlfaAesar 41907) was addedmethoxyacetic anhydride (3.7 gram, 0.0228 mol, made by the reaction ofmethoxyacetic acid and acetic anhydride). The contents of the reactionmixture were heated to 60° C. for 16 hours to give a viscous liquidmixture of the product and the by-product the ethylester ofmethoxyacetic acid. The mixture was soluble and stable in water andmethanol. The product mixture left a 10.14% ceramic oxide residue asmeasured by TGA in air.

Synthesis of Gallium(III)-Methoxyethoxyacetate

To gallium ethoxide (1.06 gram, 0.00517 mol, AlfaAesar 41907) was addedmethoxyethoxyacetic anhydride (4.16 gram, 0.0167 mol, made by thereaction of methoxyethoxyacetic acid and acetic anhydride). The contentsof the reaction mixture were heated to 60° C. for 18 hours to give aviscous liquid mixture of the product and the by-product the ethylesterof methoxyethoxyacetic acid. The mixture was soluble and stable in waterand in dilute aqueous hydrochloric acid. The product mixture containingthe ester and gallium salt left a 6.09% ceramic oxide residue asmeasured by TGA in air. IR(thin film) 2984, 2931, 2894, 1753, 1603,1457, 1204, 1145, 1101 cm⁻¹.

Synthesis of Lanthanum(III)-Methoxethoxyacetate

To lanthanum acetate (45.103 gram, 0.13 mol, AlfaAesar 11263) was addedmethoxyethoxyacetic acid (129.7 gram, 0.97 mol, Aldrich 40,701-1). Thecontents of the reaction mixture were magnetically stirred and heated to145° C. and then the by-product acetic acid as well as some of theexcess ether acid were removed by distillation to give the product(144.3 gram, 12.6% lanthanum) in methoxyethoxy acetic acid. TGA analysisof the material showed a ceramic oxide yield of 13.25%; calc 14.8%.IR(thin film) 2931, 2896, 1739, 1588, 1457, 1429, 1144, 1118 cm⁻¹.

Synthesis of Neodymium(III)-Methoxyacetate

To neodymium carbonate hydrate (10.606 gram, 0.023 mol, AlfaAesar 15301)were added methoxyacetic acid (20.0 gram, 0.22 mol, Aldrich 194557) anddeionized water (6.0 gram). The contents of the reaction mixture weremagnetically stirred and heated to 90° C. for 14 hours. Evolution of gas(presumably CO₂) was copious on heating and care should be taken onrunning similar reactions on a larger scale. The next day, the reactioncontents were cooled to give the product in a solution of free acid andwater. (32.0 gram, 10.3% neodymium). TGA analysis of the material showeda ceramic oxide yield of 14.86%. IR(thin film) 3007, 2946, 1735, 1592,1427, 1341, 1246, 1202, 1121 cm⁻¹.

Formulation of Bismuth and Lanthanum andTitanium(IV)-3,6-Dioxaheptanoate to a Water-Processable and Non-ToxicSolvent-Containing Precursor to Lanthanum-Doped Bismuth Titanate (BLT).

A BLT precursor solution was made by combining 10.08 gram of a solutionof bismuth methoxyethoxy acetate (23.9% bismuth made by the reaction ofthe free acid and triphenyl bismuth); 3.597 grams of the lanthanummethoxyethoxy acetate described above; and 13.82 grams of solution oftitanium methoxy acetate (3.99% Ti). The synthesis of triphenyl bismuthis disclosed in above-referenced U.S. Pat. No. 6,303,804, while thesynthesis of titanium methoxy acetate is disclosed in above-referencedU.S. Pat. No. 6,316,651. The BLT precursor solution having a gram-atomratio of Bi:La:Ti of 3.35:0.85:3.00 was used to make the thin film BLTferroelectric capacitors described immediately below.

Processing of Described BLT Precursor to BLT Thin Films

1. Substrate Preparation Including Bottom Electrode Evaporation.

A conventional 20 mil thick silicon wafer was prepared with 5,000 Å of awet thermal oxide (silicon). A 25 Å thick Ta adhesion layer followed bya 1,800 Å thick Pt layer were E-beam evaporated onto the substrate.Sheet resistance of the electrodes was 0.73 ohm/square. The electrodeswere pre-annealed in oxygen for 30 min at 650° C. to oxidize the Talayer and stabilize the Pt layer.

2. Deposition and Firing of Bismuth Lanthanum Titanate Thin Film onElectroded Substrate.

Wafers were coated with the BLT solution described above using a 3 to 5Krpm 30 sec spin. After coating, the wafers were slowly lowered onto a320° C. hot plate and baked for 4 minutes.

After spin coating and hot plate baking, the wafers were fired in amini-brute furnace in flowing O₂ at 700° C.

After firing, the wafers showed no signs of cracking and no adhesionfailures. SEM analysis of the dielectric films showed the surface to besmooth. Thickness measurements showed the thickness to be approximately1,100 to 1,700 Å.

3. Application of Top Electrode.

A 1,000 Å Pt top electrode was deposited through a shadow mask usingvarying top electrode sizes of approximately 10, 15, 20, 40, 80, and 160mil diameter. The stack was annealed at 700° C. for 2 hours beforeelectrical test.

4. Initial Electrical Test.

The devices were tested on an analytical prober. Contact to the topelectrode was made directly with a probe tip, contact to the bottomelectrode was made by scratching through the BLT layer with a secondprobe tip. The CV characteristics were measured using a HP4275A LCRmeter at 100 KHz using a modulation voltage of 35 mV over a wide rangeof bias voltages. The IV characteristics were measured using a HP 4145BSemiconductor Parameter Analyzer over the range of −3.5 V to +3.5 V. Fora typical 10 mil diameter shadow mask capacitor, the capacitance rangedfrom 1.69 pF at 0 V to 0.75 pF at 6.5 V. The maximum leakage current wasmeasured to be 100 nA at 3.5 V. The devices exhibited the characteristichystersis effects of ferroelectric materials, as shown in the soleFIGURE, which is a plot on coordinates of polarization and voltage.

Summary

A number of Group III polyether acid ceramic precursor materials andthin film BLT ferroelectric capacitors made from these materials havebeen disclosed.

INDUSTRIAL APPLICABILITY

The formation of Group III polyether acid ceramic precursor materials isexpected to find use in the fabrication of a number of solid statedevices, including, but not limited to, ferroelectric devices, as wellas in the fabrication of water-soluble gallium complexes.

1. A water-stable and water-soluble ceramic precursor containing atleast one Group III metal polyether acid salt complex.
 2. The ceramicprecursor of claim 1 wherein said metal polyether acid salt complexcomprises said Group III element and a polyether acid given by theformulaCH₃O(CH₂CH₂O)_(x)CH₂COOH where x is an integer of 0 to
 2. 3. The ceramicprecursor of claim 1 wherein said Group III metal poly-ether acid saltis represented by the following structure

where Metal is selected from the Group III elements, m is 3, and p isindependently 0, 1 or 2 for each of the three ligands.
 4. The ceramicprecursor of claim 3 wherein said Group III element is selected from thegroup consisting of Al, Ga, In, Tl, Sc, Y, La, lanthanides, Ac, andactinides.
 5. The ceramic precursor of claim 4 wherein said Group IIIelement is selected from the group consisting of aluminum, lanthanum,and gallium.
 6. A water-stable and water-soluble gallium polyether acidcomplex.
 7. The gallium polyether acid complex of claim 6 wherein saidpolyether acid is given by the formulaCH₃O(CH₂CH₂O)_(x)CH₂COOH where x is an integer of 0 to
 2. 8. The galliumpolyether acid complex of claim 6 wherein said gallium polyether acidsalt is represented by the following structure

where Metal is selected from the Group III elements, m is 3, and p isindependently 0, 1 or 2 for each of the three ligands.